This week’s tree climbing surveys turned up a Natterer’s bat roosting in a rot hole. It’s a good example of why getting up close to a tree can tell you so much more than looking at it from the ground.

What is a tree climbing bat survey?

Trees can have features that bats use for roosting, such as rot holes, splits, cracks and lifted bark. From the ground it’s often impossible to tell whether these features are actually being used.

On a climbed survey, our licensed ecologists climb the tree and check each potential roost feature up close, using an endoscope to look inside for bats or signs of them, such as droppings or staining.

Why climb rather than survey from the ground?

Tree climbing surveys can be a cost-effective way of assessing potential roost features:

• Features can be ruled out. Many features that look suitable from the ground turn out not to be once they’re checked up close.
• Further surveys can often be avoided. If none of the features are suitable, you may not need any more bat surveys on those trees.
• Dusk and dawn surveys can be targeted. Where further surveys are needed, they can focus on the trees and features that matter.

What happens if bats are found?

All UK bats and their roosts are protected by law. If a roost is found in a tree that will be affected by works, we’ll advise on the next steps. That might mean further surveys, changes to the design so the tree can be kept, or a licence from Natural England.

Need trees checked for bats?

Find out more about our aerial tree inspections and bat surveys, or get in touch to talk through your site.

Great work from the team this week, installing a 60 m silt curtain and oil boom in the River Great Ouse ahead of works for a new bridge crossing.

Why a silt curtain and oil boom?

Construction work in and next to a river can stir up sediment, and there’s always a risk of fuel or oil getting into the water from plant working nearby. Left unchecked, either can travel a long way downstream and harm fish and other wildlife.

• The silt curtain hangs down into the water like a floating screen, holding back muddy water so the sediment settles within the works area instead of spreading downstream.
• The oil boom floats on the surface and contains any fuel or oil before it can spread.

Together they protect water quality and the river beyond the site while the bridge works go ahead.

Getting it in place

Installing 60 m of barrier in a working river is a job for the boat. Our crew set out the curtain and boom from the workboat and fixed everything in position. Two things made a big difference:

• Lower summer flows, which make the river easier and safer to work on
• A 2 tonne concrete block, a giant Lego-style anchor that holds everything firmly in place

Working on your river project

We provide safety boat and workboat support for construction, maintenance and survey work on rivers, canals, lakes and the coast, with RYA Powerboat Level 2 qualified, first aid trained crew. Where works also need ecology support, such as fish rescues during dewatering, we can cover both. Get in touch to talk through your project.

eDNA has become a popular tool in ecological surveys, and it has its place. But it isn’t the silver bullet it’s sometimes made out to be, particularly in rivers.

We recently carried out a white-clawed crayfish survey by hand search and found crayfish within the project area itself. That’s the information a planning decision actually needs: are they here, where exactly, and how will the works affect them?

The problem with eDNA in rivers

eDNA (environmental DNA) works by sampling the water for traces of DNA that animals shed into their surroundings. It’s a clever technique, but in a river there’s a basic limitation: water moves, and DNA drifts downstream with it.

A positive result tells you the species is somewhere in the catchment above your sampling point. It doesn’t tell you whether it’s in your works footprint, 50 metres upstream or a kilometre away. In a river, how do you know where the source is?

Sometimes the answer is obvious. When the Rivers Trust ran eDNA fish surveys on the River Irwell, the results showed tuna to be present. We think it’s safe to say the source on that one was a tin of John West.

Where eDNA works well

None of this means eDNA isn’t useful. It’s excellent for:

• screening and scoping large areas quickly
• checking whether a species is likely to be present in a catchment
• flagging where to focus more detailed survey effort

Why hand searches still matter

For project-specific questions, the exact location of a species drives everything that follows: the impact assessment, the mitigation and any licensing. White-clawed crayfish are a protected and declining species, so getting that right matters for both the crayfish and the project programme.

A licensed surveyor in the water can tell you exactly where crayfish are, how many there are and what habitat they’re using. That’s the detail you need to design mitigation that works and to avoid delays later on.

Need a white-clawed crayfish survey?

Our licensed ecologists carry out white-clawed crayfish surveys across most of the UK, alongside fish surveys and fish rescues for works in and around water. Get in touch and we’ll advise on the right approach for your site.